JPS60141818A - Production of dead soft steel by vacuum degassing treatment - Google Patents

Abstract

PURPOSE:To decarburize and refine a molten steel to a dead soft steel without decrease in yield owing to splashes as in gaseous oxygen blowing in the stage of decarburizing and refining the molten steel with a vacuum degassing device by adding the oxide of iron into the molten steel. CONSTITUTION:The suction nozzle and discharge nozzle of an RH type vacuum degassing vessel 2 are dipped into the molten steel 4 in a ladle 5. The interior of the vessel 2 is evacuated to <=200Torr by an evacuating pipe 3 and a molten steel 4 is circulated by the suction nozzle and discharge nozzle through the vessel 2 and the ladle 5. The oxide of iron such as mill scale, etc. is added through a feed port 1 at a rate of 0.1-8kg per ton of the molten steel and is brought into reaction with C in the steel 4 so that the C is evaporated and removed in the form of CO. The molten steel is thus decarburized. Since oxygen is added in the form of solid oxide to the steel, the scattering loss of the molten steel owing to splashes as in the case of gaseous oxygen blowing is eliminated and the dead soft steel of <10ppm C is stably produced at a high yield.

Description

【発明の詳細な説明】 （産業上の利用分野） この発明は、真空脱ガス装置、たとえばＲＨ，ＤＨなど
での溶鋼の真空脱ガス処理に関するものである。DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to vacuum degassing treatment of molten steel in a vacuum degassing apparatus, such as RH or DH.

（従来技術） 従来の極低炭素鋼の製造方法としては、溶銑を転炉で吹
錬後、真空脱ガスによる自然脱炭または槽内へ酸素を吹
きこむ強制脱炭である。極低炭素鋼溶製のだめの真空脱
ガス処理方法に関してはいくつかの文献が公表されてい
る。例えば、検氷等は、鉄と鋼（Ｖｏｌ、　６３．Ａｌ
　３　、１９７７　）に環流ガス（１） のＡｒの二段吹込みの結果を発表している。この結果に
よると脱炭速度が上昇し安定して極低炭素鋼の溶製が可
能となっている。しかしながら、環流ガスのＡｒの二段
吹込みは、浸漬管の構造が複雑となシ、また操業上も環
流ガスの吹込位置が浅くなるのは好ましくない。また川
崎製鉄株式会社が製鋼部会（１９８１）で「転炉−ＲＨ
法による極低炭素鋼の溶製」と題し、１５　ｐｐｍの極
低炭素鋼の溶製技術を確立したと発表している。この結
果をみると、環流ガス量を１５００　Ｎｌ／ｎ１１ｎか
ら５０００１Ａｎｌｎ　ヘ増加し、スプラッシュによる
寄与で極低炭素鋼を溶製している。しかしながら、この
ような環流ガスの大量吹込みはスプラッシュの増大にょ
る脱炭速度の上昇をもたらすが、真空槽内の地金付きも
また増大するため、操業上合金歩留の不安定や、鉄分歩
留のロスまた真空槽内に付着した地金を除去するための
休止などの問題点が生ずる。同様に酸素を吹きこむ強制
脱炭においても酸素を吹くため槽内へのスプラッシュの
飛散が多くなシ、操業上問題となる。(Prior Art) Conventional methods for producing ultra-low carbon steel include natural decarburization by vacuum degassing after hot metal is blown in a converter, or forced decarburization by blowing oxygen into a tank. Several documents have been published regarding vacuum degassing treatment methods for molten ultra-low carbon steel pots. For example, ice detection etc.
3, 1977) published the results of two-stage Ar injection into the reflux gas (1). The results show that the decarburization rate increases and stable production of ultra-low carbon steel becomes possible. However, the two-stage Ar injection of the reflux gas requires a complicated structure of the immersion pipe, and it is not preferable for the reflux gas to be blown into a shallow position in terms of operation. In addition, Kawasaki Steel Co., Ltd., in the Steelmaking Subcommittee (1981)
Titled ``Production of ultra-low carbon steel by the method,'' the company announced that it had established a technology for producing ultra-low carbon steel with a concentration of 15 ppm. Looking at this result, the amount of recirculated gas was increased from 1500 Nl/n11n to 50001 Anln, and ultra-low carbon steel was melted due to the contribution from splash. However, although the injection of such a large amount of recirculated gas increases the decarburization rate due to the increase in splash, it also increases the amount of metal stuck inside the vacuum chamber, leading to instability in the alloy yield during operation and problems with iron content. Problems arise, such as a loss in yield and a stoppage to remove the metal deposited in the vacuum chamber. Similarly, in forced decarburization by blowing oxygen, there is a lot of splash in the tank due to the blowing of oxygen, which poses operational problems.

（２） すなわち、従来技術としては、環流ガスの吹込み方法の
改良や吹込みガス量を増大させて極低炭素鋼を得る。ま
たは、酸素吹込みによる強制脱炭があげられる。(2) That is, as a conventional technique, ultra-low carbon steel is obtained by improving the method of blowing the circulating gas or increasing the amount of blowing gas. Another option is forced decarburization by oxygen injection.

本発明の真空脱ガス処理方法は、鉄系酸化物を真空槽内
に添加し、これによって溶鋼中の溶解酸素量を増大させ
て極低炭素鋼を得るという点で従来技術とは基本的に異
なる。従来の自然脱炭による環流ガスの吹込み方法の改
良や環流ガス量の増大などは行−なわず、酸素を吹込む
強制脱炭のスジラッシュ増大による槽内地金付着を防止
した。鉄系酸化物を固体状態で真空槽内に添加し、溶解
酸素量をコントロールして極低炭素鋼を得るものである
。すなわち脱炭のために固体酸化物である鉄系酸化物を
真空槽内に添加するという点で明らかに別の発明思想と
いうことができる。The vacuum degassing method of the present invention is fundamentally different from conventional technology in that iron-based oxides are added to the vacuum chamber, thereby increasing the amount of dissolved oxygen in molten steel to obtain ultra-low carbon steel. different. We did not improve the method of blowing the recirculated gas or increase the amount of recirculated gas in the conventional natural decarburization process, but instead we prevented metal deposition inside the tank due to the increased streak rush of the forced decarburization process in which oxygen was injected. Iron-based oxide is added in a solid state to a vacuum chamber, and the amount of dissolved oxygen is controlled to obtain ultra-low carbon steel. That is, it can be said that this invention is clearly a different idea in that an iron-based oxide, which is a solid oxide, is added to the vacuum chamber for decarburization.

（発明の目的） 本発明は、従来技術にはみられない鉄系酸化物を真空槽
内に添加することによシ脱炭速度を上昇させ、従来問題
となっているスジラッシュの飛散を著しく減少させて極
低炭素鋼を得ることを目的とするものである。(Purpose of the invention) The present invention increases the decarburization rate by adding iron-based oxides, which are not found in the prior art, into the vacuum chamber, and significantly reduces the scattering of streak lash, which has been a problem in the past. The purpose is to obtain ultra-low carbon steel by reducing the carbon content.

（発明の構成・作用） 本発明は、２００Ｔｏｒｒ以下の減圧下の溶鋼に鉄系酸
化物を０．１　ｋｖＴ以上８ｋｇ／Ｔ以下の範囲で真空
槽内に添加することを特徴とする溶鋼の真空脱ガス処理
方法である。ここでは、例としてＲＨでの処理の場合を
説明する。(Structure and operation of the invention) The present invention is characterized in that an iron-based oxide is added to molten steel under a reduced pressure of 200 Torr or less in a vacuum chamber in a range of 0.1 kvT or more and 8 kg/T or less. This is a degassing treatment method. Here, a case of processing in RH will be explained as an example.

第１図は、本発明のＲＨでの処理を示したもので、１は
合金投入シーート、２は真空脱ガス槽、３は排気口、４
は溶鋼、５は取鍋である。本発明は真空脱ガス槽２へ鉄
系酸化物を添加し溶鋼４と反応させて脱炭を促進するこ
とを特徴とし添加は合金投入シーート１よシ行なう。す
なわち合金投入シュート１よシ真空脱ガス槽２へ鉄系酸
化物を添加し、溶鋼４と反応させて溶鋼４に含有する炭
素の脱炭を促進し、極低炭素鋼を得る。得られる極低炭
素鋼の炭素レベルは、上記処理方法による真空処理　゛
脱炭時間１０分で２０　ｐｐｍ　、　１５分で１０ｐｐ
ｍとなり、安定して極低炭素鋼の製造が可能である。Figure 1 shows the RH treatment of the present invention, where 1 is an alloy charging sheet, 2 is a vacuum degassing tank, 3 is an exhaust port, and 4 is a vacuum degassing tank.
is molten steel, and 5 is a ladle. The present invention is characterized in that iron-based oxides are added to the vacuum degassing tank 2 and reacted with the molten steel 4 to promote decarburization, and the addition is carried out through the alloy input sheet 1. That is, an iron-based oxide is added to the vacuum degassing tank 2 through the alloy charging chute 1, and is reacted with the molten steel 4 to promote decarburization of carbon contained in the molten steel 4, thereby obtaining ultra-low carbon steel. The carbon level of the obtained ultra-low carbon steel is 20 ppm after 10 minutes of decarburization and 10 ppm after 15 minutes of vacuum treatment using the above treatment method.
m, making it possible to stably produce ultra-low carbon steel.

このような極低炭素鋼は、最近自動車用外板の成形の難
しい材料としての超深絞シ用鋼板として需要があυ、炭
素レベルを低くすることが深絞シ性を得るために必要で
ある。These ultra-low carbon steels have recently been in demand as steel sheets for ultra-deep drawing, which is a difficult-to-form material for automobile outer panels, and lowering the carbon level is necessary to obtain deep drawing properties. be.

この発明は、１０ｐｐｍ程度の極低炭素鋼の製造を鉄系
酸化物の添加によって行なうことを特徴とするが、従来
法に比べて真空槽内に飛散するスプラッシーが著しく低
減され、真空槽内に付着する地金が大巾に減少する。す
なわち、真空槽内に地金が付着すると、成分調整のため
に添加する合金を添加しても歩留が悪くなり成分調整が
困難になり、処理を中断して付着した地金を除去しなけ
ればならない。これはＲＨの稼動率を下げることになシ
、生産上の障害となる。本発明は、鉄系酸化物を真空槽
内に添加するため、スジラッシュが増加するということ
はな（、ＲＨの安定操業を可能にできるという点におい
ても極めて優れている。This invention is characterized by manufacturing ultra-low carbon steel of about 10 ppm by adding iron-based oxide, but compared to conventional methods, the amount of splash that scatters inside the vacuum chamber is significantly reduced. The amount of metal attached to the metal is drastically reduced. In other words, if metal adheres to the inside of the vacuum chamber, even if alloys are added to adjust the composition, the yield will deteriorate and it will be difficult to adjust the composition, and the process will have to be interrupted to remove the adhered metal. Must be. This does not reduce the operating rate of the RH and becomes a hindrance to production. Since the present invention adds iron-based oxides to the vacuum chamber, there is no increase in streak rush (and it is also extremely excellent in that it enables stable RH operation.

本発明は、２００Ｔｏｒｒ以下の減圧下で顕著に脱炭速
度の向上、極低炭素鋼の製造という点で効果が見られた
。真空度が２００Ｔｏｒｒ以上では脱炭速度（５） が遅く、極低炭素鋼を得るには長時間を要し、従来法と
の比較では差が認められない。The present invention was found to be effective in significantly improving the decarburization rate and producing ultra-low carbon steel under reduced pressure of 200 Torr or less. When the degree of vacuum is 200 Torr or more, the decarburization rate (5) is slow and it takes a long time to obtain ultra-low carbon steel, and no difference is observed when compared with the conventional method.

鉄系酸化物の添加量については第２図に鉄系酸化物とし
てミルスケールの添加量と溶鋼中の溶解酸素量の関係を
表わしている。鉄系酸化物としては、ミルスケールのよ
うなウスタイト、ヘマタイト、マグネタイトを含有する
ものでよく、第２図に示すようにミルスケールの添加量
の増大にともない溶解酸素量が増大し、脱炭速度を上昇
させ、極低炭素鋼が得られる。溶解酸素量を増大させて
、脱炭速度を上昇させる効果はわずかのミルスケールの
添加で確認され、０．１　ｋｌｉｌ／Ｔがら８　ｋｇ／
Ｔの範囲の添加で脱炭速度が上昇した。８　ｋｇ／Ｔ以
上の添加量としても溶解酸素量が増大するが、溶鋼の温
度降下が大きく、液相線近傍の温度まで低下してしまう
ことによシ、脱炭時間を確保できないという問題がある
。Regarding the amount of iron-based oxide added, FIG. 2 shows the relationship between the amount of mill scale added as iron-based oxide and the amount of dissolved oxygen in molten steel. The iron-based oxide may be one containing wustite, hematite, or magnetite such as mill scale, and as shown in Figure 2, as the amount of mill scale added increases, the amount of dissolved oxygen increases, and the decarburization rate increases. By increasing the carbon content, ultra-low carbon steel can be obtained. The effect of increasing the amount of dissolved oxygen and increasing the decarburization rate was confirmed by adding a small amount of mill scale, from 0.1 klil/T to 8 kg/T.
The decarburization rate increased with the addition of T in the range. Even if the addition amount is 8 kg/T or more, the amount of dissolved oxygen increases, but the temperature drop of the molten steel is large and the temperature drops to near the liquidus line, which causes the problem that decarburization time cannot be secured. be.

本発明は、ＲＩ（の他の真空処理設備、たとえばＤＨ、
ＶＡＤなどにおいても極低炭素鋼を得るための真空脱ガ
ス処理方法である。すなわち、鉄系酸化（６） 物の添加による溶鋼中の溶解酸素量をコントロールして
脱炭速度を上昇させ、極低炭素鋼を得るという処理方法
である点から、ＤＨやＶＡＤなどの他の真空処理設備に
おいても有効である。The present invention applies to RI (other vacuum processing equipment such as DH,
It is also a vacuum degassing treatment method for obtaining ultra-low carbon steel in VAD and the like. In other words, it is a processing method that increases the decarburization rate by controlling the amount of dissolved oxygen in molten steel by adding iron-based oxidants (6) to obtain ultra-low carbon steel. It is also effective in vacuum processing equipment.

（実施例） 本発明の鉄系酸化物を真空槽内に添加する処理方法と従
来法との脱炭挙動を第３図に示す。第３図に示すように
、本発明では、脱炭時間１５分で８ｐｐｍの極低炭素鋼
が得られている。処理条件を下記に示す。(Example) FIG. 3 shows the decarburization behavior of the treatment method of adding the iron-based oxide of the present invention into a vacuum chamber and the conventional method. As shown in FIG. 3, according to the present invention, ultra-low carbon steel with a carbon content of 8 ppm is obtained with a decarburization time of 15 minutes. The processing conditions are shown below.

処理溶鋼量　２４５Ｔ 脱炭時間　１５分 上記に示すように、この発明は、鉄系酸化物を槽内添加
することによシ極低炭素鋼が得られ、スプラッシュの飛
散も著しく少々くなっている。Amount of molten steel processed: 245 T Decarburization time: 15 minutes As shown above, in this invention, an extremely low carbon steel is obtained by adding iron-based oxides in the tank, and the amount of splashing is significantly reduced. .

（発明の効果） 本発明は、従来法の欠点であるスプラッシュの飛散の増
大による真空槽内の地金付着の問題を有利に解決し、さ
らに到達する炭素レベルもよシ低いレベルとなシ、安定
して１０ｐｐｍ程度の極低炭素鋼の溶製が可能となる。(Effects of the Invention) The present invention advantageously solves the problem of metal adhesion inside the vacuum chamber due to increased splashing, which is a drawback of the conventional method, and furthermore, the carbon level reached is much lower. It becomes possible to stably produce ultra-low carbon steel with a carbon content of about 10 ppm.

【図面の簡単な説明】[Brief explanation of drawings]

第１図は本発明の概要図、第２図はミルスケール投入量
と溶鋼中の溶解酸素量変化を示す図、第３図は脱炭推移
を示す図でおる。 １：合金投入シュート　２：真空脱ガス槽３：排気口　
４：溶鋼 ５：取鍋 第１ ］ 〕 ７３− ／′ 一（FIG. 1 is a schematic diagram of the present invention, FIG. 2 is a diagram showing changes in the amount of mill scale input and the amount of dissolved oxygen in molten steel, and FIG. 3 is a diagram showing the decarburization transition. 1: Alloy charging chute 2: Vacuum degassing tank 3: Exhaust port
4: Molten steel 5: Ladle No. 1 ] ] 73- /' 1 (

Claims (1)

【特許請求の範囲】[Claims] ２００　Ｔｏｒｒ以下の減圧下の溶鋼に鉄系酸化物を０
、１　ｋｇ／Ｔ以上８　ｋｇ／Ｔ以下の範囲で真空槽内
添加することを特徴とする溶鋼の真空脱ガス処理による
極低炭素鋼の製造方法。Zero iron-based oxides are added to molten steel under reduced pressure of 200 Torr or less.
, a method for producing ultra-low carbon steel by vacuum degassing treatment of molten steel, characterized by adding in a vacuum tank in a range of 1 kg/T or more and 8 kg/T or less.